Coating flexible sheets



- Patented Feb, 7, 1939 I COATING FLEXIBLE SHEETS Walter Durgin Bowlby,Jersey City, N. J., assignor to Egyptian Lacquer Manufacturing Company,a. corporation of New Jersey No Drawing. Application November 5, 1935,

Serial No. 48,285

3 Claims. or 91-68) This invention relates to, coating flexible fibroussheets and is particularly concerned with the production of coatingcompositions for paper and the like. More specifically, the inventioncon- 5 templates improvements in lacquers and in lacquered papers.

It has been recognized heretofore that the viscosity characteristic ofnitrocellulose decreased with the degree of degeneration of thenitrocellulose, and that if the nitrocellulose were sufficientlydegenerated more of it could be dissolved in a given amount of solventwithout making the resulting solution too viscous for use. However, asthe degree of degeneration of nitrocellulose increases, the materialsuffers a physical change:

and it has been the general view, heretofore accepted, thatnitrocellulose having an exceedingly low viscosity characteristic was anundesirable lacquer ingredient, unless it was used together with otherand less degenerated nitrocellulose having a higher viscositycharacteristic.

It has also been customary to employ nitrocellulose having a relativelyhigh nitrogen content, say from 11.5% up, in the manufacture oflacquers, and standard works onthe subject state that lacquers must bemade with nitrocellulose having a nitrogen content from 11.5 to 12%.

As a result of my investigations I have discovered that lacquers inwhich the nitrocellulose content has an exceedingly low averageviscosity characteristic, i. e. below 50 centipoises, is an admirablecoating composition for paper and other flexible fibrous sheets. Suchlacquers pos-' sess great adhesiveness and form desirable coat-- ings onpaper. Coatings on paper-etc. resulting from the practice of myinvention are durable, lustrous, flexible and hard. Moreover, thepractice of my invention permits the production of lacquered paperswhich manifest substantially no tendency to curl,- shrink or wrinkle.This tendency to curl is an undesirable characteristic of lacqueredpaper made in accordance with prior proposals.

Throughout the application and appended claims I use the term paper toinclude cardboard, wrapping, sheets, and other flexible fibrous sheetmaterial.

I- have also discovered that nitrocellulose hav- 50 ing a nitrogencontent of from 10 to 11% is partlcularly desirable in themanufacture oflacquer intended for coating paper food wrappers or containers, in thatnitrocellulose of this character is completelysoluble in alcohols, suchas ethyl,

55 methyland butyl alcohols, and when so dissolved will forrriT asubstantially odorless and non-toxic film on paper. Nitrocellulosehaving a nitrogen content substantially belo'w'10% 01: substantially-'above'11% isnotcolnpletdysolubleinthecom-;monalcchob,andhenc'eslmnlrlnotbeusedin conjunction with alcohol as asingle active solvent.

By viscosity characteristic of nitrocellulose, I mean thedegree ofviscosity which a given sample of nitrocellulose will impart to a givenamount 5 of a standard solvent, as expressed in centipoises. Throughoutthe specification and the appended claims, the figures for viscositycharacteristic are as determined-by the following method:

A solution containing 12% by weight of nitro- 10' cellulose in a solventconsisting of three parts butyl acetate and one part ethyl alcohol isprepared, and the viscosity of the solution in centipoises isdetermined,preferably in a viscosimeter of the capillary tube type, or by otherstandard 15 methods. The resulting determination in centipoises is takenas the viscosity characteristic of the nitrocellulose in the solution.

In ,accordance with the principles set forth above, my inventioncontemplates an improved 20 coating composition for paper and the like,comprising nitrocellulose having a viscosity characteristic of from 1 to50 centipoises, and a solvent therefor. My invention provides a novelcurl-resistant sheet comprising paper or other 25 flexible fibrousmaterial having a coating, the nitrocellulose content of which has anaverage viscosity characteristic ranging from 1 to 50 centipoises. Myinvention further provides substantially odorless and non-toxic coatingson paper 30 and the like, said coatings containing nitrocellulose havingan average nitrogen content ranging from 10 to 11%. When paper wrappingsor the like for food products are to be manufactured I prefer to combinethe advantages of low vis- 35 cosity characteristic and relatively lownitrogen content of nitrocellulose.

The degree of flexibility and the velvet feel of dried lacquer filmsmade in accordance with my invention may be increased, if desired, by 40incorporating softening agents into the fluid lac quer. Any of thecustomary softening agents may be employed, but I have found that rawcastor oil, dibutyl phthalate, triethyl citrate, butyl phthalyl butylglycollate, and mixtures of these compounds are particularly desirable.

The resistance to friction of dried films of lacquer made in accordancewith my invention may be decreased by incorporating petroleum jelly,fats or-waxes into the fluid lacquer. When the lacquer is intended forcoating wrappers adapted to machine packaging, a low resistance tofriction or high slip is desirable, and I have found that a small amountof petroleum jelly,

say 5% or less by weight of the fluid lacquer, is J desirable forimparting this characteristic.

If required, crystallizing agents, (his, solid pigments, bronze powders,or other agents for producing special appearances may be incorporatedinto the lacquer of my invention. co

My invention will be better understood in the light of the followingformulae for lacquers made in accordance therewith.

Formula 1 Parts by weight Nitrocotton (viscosity characteristic 1-50\centipoises) 25 Raw castor oil 15 Dibutyl phthalate Ethyl alcohol Total10o Formula 2 Parts by weight Parts byweight Nitrocotton (viscositycharacteristic 1-50 centipoises) 45 Butyl phthalyl butyl glycollateu 20Alcohol 15 Methyl ethyl ketone l0 Petroleum spirits 10 Total Thepreparation of the lacquers of my invention (as illustrated in theforegoing formulae) requires no special procedure or apparatus andv maybe conducted in any of the customary ways. As shown by the foregoingexamples, the solid content of lacquers prepared in accordance with myinvention may be unusually high, thus permitting a great economy in theuse of solvents, and enabling lacquers to replace spirit varnishes andsimilar materials in the coating of paper and the like. As compared withvarnishes, lacquers prepared in accordance with my invention offer thefollowing advantages in coating paper: (1) Freedomfrom residual odor,

(2) Greater adhesion to the paper, (3) Increased resistance to marring,scufflng and cracking, Greater fluidity and ease of application,Increased speed of drying, Thicker coatings, if desired, Lessdiscoloration of the paper, Higher-gloss, and Better feel.

(4) (5) (6) ('7) (8) (9) 1 Lacquers prepared in accordance with theforegoing formulae do not cause paper to shrink, wrinkle or curl whenthey are applied thereto. A lacquer which is particularly desirable forcoating paper intended for wrappers or containers of food has-thefollowing formulae:

Formula 4 Parts by weight Nitrocotton (nitrogen content 10.5%, viscosi--This lacquer dries quickly into a lustrous uniform film having greatadhesiveness and resistance to scumng. It has a high slip and may beused to coat papers intended for use in automatic packaging machines.when dry it is practically odorless and non-toxic. It does not cause thepaper to which it is-applied to shrink, curl, or wrinkle. I

When residual odor or slight toxicity are unobjectionable in theproduct, many other solvents may be employed. Thus, acetone or amylacetate may be employed as active solvents, and toluol, butyl aldehydeetc. may be used as diluents.

The lacquers of my invention may be applied to paper in the same mannerthat varnish etc. are customarily applied. Reverse roll machines, knifecoaters and various kinds of rolls may be used.

My lacquers may be used to coat printed papers, transparent papers,colored papers, etc. when used in thick films on printed paper a coatingis formed which is comparable in appearance and utility with aregenerated cellulose wrapping. Moreover, the cost of such films is lessthan half the cost of equivalent cellulose wrapping sheets,

and there is a further saving in that the separate wrapping operationwith the transparent sheet is eliminated.

In general, I have foundthat the gloss of lacquer films on paperincreases as the average viscosity characteristic of the nitrocellulosein the lacquer decreases. There is no decrease in the apparent strength,flexibility, or adhesiveness of the film as the viscosity characteristicof its nitrocellulose content is decreased below 50 centipoises, andfilms in which the total nitrocellulose content has a viscositycharacteristic of only one centipoise are useful. I attribute theapparent strength, toughness, flexibility and durability of theselacquer films on paper to the remarkable adhesion between the fibrouspaper backing and the lacquer film, whereby the film and the paper areenabled to cooperate and the tensile strength of the paper is impartedto the whole mass.

Nitrocellulose which has been degenerated in any of the customarymethods'may be employed in the practice of my invention, provided thatits viscosity characteristic is sufficiently low. Thus, nitrocottondegenerated by heat and pressure or by alkaline or acid reagents may beused, provided such nitrocellulose has a viscosity characteristicranging from 1 to 50 centipoises, a range which was heretoforeconsidered substantially useless.

It will be understood that the practice of my invention is not limitedto the use of the specific solvents, diluents. softening agents, andcrystallizing agents, nor to particular proportions of the variousingredients set forth in the formulae.

I claim:

1. A flexible composite sheet comprising a flexible paper base and acovering film containing essentially nitro-celluiose of such degree ofdegeneration that in solution the average viscosity characteristic ofall of the nitro-cellulose ranges from 1 to 50 centipoises and isinherently brittle in film form, said film adhering to the paper basewith a tenacity suillclent to overcome its inherent tendency to crackandscparate from the paper when the latter is flexed.

2. A composite flexible sheet comprising a flexible paper base and acovering film containing essentially alcohol-soluble nitro-cellulosecontaming not substantially less than 10% o stantially more than 11%nitrogen and of such degree of degeneration that in solution the averageviscosity. characterlsticof all of the nitrocellulose ranges'from 1 to50 centipoises'and is inherently brittle in film form, said filmadhering to the paper base 'with a tenacity suflicient to overcome itsinherent tendency to crack and separate from the paper when the latteris flexed.

3. A flexible composite sheet comprising a paper base and a coveringfilm containing the nonvolatile constituents from a coating compositionwhich is substantially free from resin, comprising to 45% ofnitro-cellulose containing not substantially less than 10% norsubstantially more than 11% nitrogen and or such degree of degenerationthat in solution it has an average viscosity characteristic of from 1 to50 centipoises is'inherently brittle in mm form, from 20% to 01 asoftener, and from to of.

WALTZR DURGIN BOWLBY. 10v

